Lithographic apparatus and device manufacturing method with reduced scribe lane usage for substrate measurement

ABSTRACT

In a device manufacturing method and lithographic apparatus wherein a pattern is transferred from a patterning device onto a substrate, a measurement target is provided on the substrate in a process enabling execution of a substrate measurement using radiation of a first wavelength. Subsequently the measurement target is transformed in a grid of conducting material, the grid having grid openings which are smaller than the first wavelength. The space in the scribe lane where the measurement target was, is now shielded and may be used again in further layers or processing steps of the substrate.

FIELD OF THE INVENTION

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device in which measurements are performed forvarious purposes, such as overlay, critical dimension (CD) andalignment. For the measurements, targets are being used on thesubstrate, and measurements are executed using radiation of a predefinedwavelength (range) and a suitable detector.

DESCRIPTION OF THE RELATED ART

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.including part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude steppers, in which each target portion is irradiated by exposingan entire pattern onto the target portion at one time, and scanners, inwhich each target portion is irradiated by scanning the pattern througha radiation beam in a given direction (the “scanning” direction) whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection. It is also possible to transfer the pattern from thepatterning device to the substrate by imprinting the pattern onto thesubstrate.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist) bythe changes of either optical properties or surface physical propertiesof the resist. Alternatively, the imaging may use a resistless processsuch as etched grating or nano-imprint technology. Prior to thisimaging, the substrate may undergo various procedures, such as priming,resist coating and a soft bake. After exposure, the substrate may besubjected to other procedures, such as a post-exposure bake (PEB),development, a hard bake and measurement/inspection of the imagedfeatures. This array of procedures is used as a basis to pattern anindividual layer of a device, e.g. an IC. Such a patterned layer maythen undergo various processes such as etching, ion-implantation(doping), metallization, oxidation, chemical-mechanical polishing, etc.,all intended to finish off an individual layer. If several layers arerequired, then the whole procedure, or a variant thereof, will have tobe repeated for each new layer. Eventually, an array of devices will bepresent on the substrate (wafer). These devices are then separated fromone another by a technique such as dicing or sawing, whence theindividual devices can be mounted on a carrier, connected to pins, etc.

The measurement and inspection after development of the resist (orsubstrate surface in the case of etching), referred to as in-linebecause it is carried out in the normal course of processing productionsubstrates, is used, for example, to measure overlay between twosequential processes in the lithography apparatus using measurementtargets in the scribe lanes between the devices. Several methods may beused and may include measurement of overlay subsequently in two(perpendicular) directions on the substrate surface, or directmeasurement using a complex two dimensional measurement target.

In each process, in general a different piece of scribe lane space isused for the measurement, in order to exclude any possible error due tointerference with measurement targets from measurements in previousprocesses.

SUMMARY OF THE INVENTION

It is desirable to provide an overlay measurement method for alithographic apparatus in which the measurements require less “realestate” on the substrate.

According to an embodiment of the invention, there is provided alithographic apparatus arranged to transfer a pattern from a patterningdevice onto a substrate, wherein the lithographic apparatus isconfigured to provide a measurement target on the wafer enabling asubstrate measurement for a specific process using a first wavelength,and to transform the measurement target in a grid of conductingmaterial, the grid having grid openings which are smaller than the firstwavelength.

According to an embodiment of the invention, there is provided a devicemanufacturing method including transferring a pattern from a patterningdevice onto a substrate, wherein the method includes providing ameasurement target on the substrate in a process enabling execution of asubstrate measurement using radiation of a first wavelength, andtransforming the measurement target in a grid of conducting material,the grid having grid openings which are smaller than the firstwavelength.

According to another embodiment of the invention, there is provided adevice manufactured according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 depicts a simplified schematic view of a scatterometryarrangement which may be used to measure asymmetry according to anembodiment of the present invention;

FIG. 3 depicts a schematic view of a scatterometry arrangement which maybe used in a lithographic apparatus according to an embodiment of thepresent invention;

FIG. 4 depicts a sectional view of a reference grating and a measurementgrating in a substrate applied in a method embodiment of the presentinvention;

FIG. 5 depicts a top view of a scribe lane used for substratemeasurements in (a) a sequential manner and (b) according to anembodiment of the present invention;

FIG. 6 depicts a top view of a grid applied to obscure a measurementtarget of an earlier measurement; and

FIG. 7 depicts a cross sectional view of a substrate in which thepresent invention is applied.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus includes an illuminationsystem (illuminator) IL configured to condition a radiation beam B (e.g.UV radiation or DUV radiation). A support (e.g. a mask table) MT isconfigured to support a patterning device (e.g. a mask) MA and isconnected to a first positioner PM configured to accurately position thepatterning device in accordance with certain parameters. A substratetable (e.g. a wafer table) WT is configured to hold a substrate (e.g. aresist-coated wafer) W and is connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters. A projection system (e.g. a refractive projectionlens system) PS is configured to project a pattern imparted to theradiation beam B by patterning device MA onto a target portion C (e.g.including one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, todirect, shape, and/or control radiation.

The support supports, e.g. bears the weight of, the patterning device.It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support can usemechanical, vacuum, electrostatic or other clamping techniques to holdthe patterning device. The support may be a frame or a table, forexample, which may be fixed or movable as required. The support mayensure that the patterning device is at a desired position, for examplewith respect to the projection system. Any use of the terms “reticle” or“mask” herein may be considered synonymous with the more general term“patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives radiation from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDincluding, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL mayinclude various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support (e.g., mask table MT), and ispatterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam B, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

-   1. In step mode, the mask table MT and the substrate table WT are    kept essentially stationary, while an entire pattern imparted to the    radiation beam is projected onto a target portion C at one time    (i.e. a single static exposure). The substrate table WT is then    shifted in the X and/or Y direction so that a different target    portion C can be exposed. In step mode, the maximum size of the    exposure field limits the size of the target portion C imaged in a    single static exposure.-   2. In scan mode, the mask table MT and the substrate table WT are    scanned synchronously while a pattern imparted to the radiation beam    is projected onto a target portion C (i.e. a single dynamic    exposure). The velocity and direction of the substrate table WT    relative to the mask table MT may be determined by the    (de-)magnification and image reversal characteristics of the    projection system PS. In scan mode, the maximum size of the exposure    field limits the width (in the non-scanning direction) of the target    portion in a single dynamic exposure, whereas the length of the    scanning motion determines the height (in the scanning direction) of    the target portion.-   3. In another mode, the mask table MT is kept essentially stationary    holding a programmable patterning device, and the substrate table WT    is moved or scanned while a pattern imparted to the radiation beam    is projected onto a target portion C. In this mode, generally a    pulsed radiation source is employed and the programmable patterning    device is updated as required after each movement of the substrate    table WT or in between successive radiation pulses during a scan.    This mode of operation can be readily applied to maskless    lithography that utilizes programmable patterning device, such as a    programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

One or more properties of the surface of a substrate 6 may be determinedusing a scatterometer arrangement such as that depicted in FIG. 2. Thescatterometer may includes a broadband (white light) radiation source 2,which directs radiation onto a substrate 6. An extended broadbandradiation source may be configured to provide the radiation beam with awavelength of at least 50 nm to the substrate surface. The reflectedradiation is passed to a spectrometer detector 4, which measures aspectrum 10 (intensity as a function of wavelength) of the specularreflected radiation.

The scatterometer may be a normal-incidence scatterometer or an obliqueincidence scatterometer. Variants of scatterometry may also be used inwhich the reflection is measured at a range of angles of a singlewavelength, rather than the reflection at a single angle of a range ofwavelengths.

In one or more embodiments described below, there is used ascatterometer configured to measure a property of a substrate 6 bymeasuring, in a pupil plane 40 of a high NA lens, a property of anangle-resolved spectrum reflected from the substrate surface 6 at aplurality of angles and wavelengths as shown in FIG. 3. Thescatterometer includes a radiation source 2 configured to projectradiation onto the substrate and a detector 32 configured to detect thereflected spectra. The pupil plane is the plane in which the radialposition of radiation defines the angle of incidence and the angularposition defines the azimuth angle of the radiation and anysubstantially conjugate plane. The detector 32 is placed in the pupilplane of the high NA lens. The NA is high and, in an embodiment, atleast 0.9 or at least 0.95. Immersion scatterometers may even havelenses with an NA over 1.

Previous angle-resolved scatterometers have only measured the intensityof scattered light. An embodiment of the present invention allowsseveral wavelengths to be measured simultaneously at a range of angles.The properties measured by the scatterometer for different wavelengthsand angles may include the intensity of transverse magnetic (TM) andtransverse electric (TE) polarized light and the phase differencebetween the TM and TE polarized light.

The light source 2 is focused using lens system L2 through interferencefilter 30 and is focused onto substrate 6 via a microscope objectivelens L1. The radiation is then reflected via partially reflectivesurface 34 into a CCD detector 32 in the back projected pupil plane 40in order to have the scatter spectrum detected. The pupil plane 40 is atthe focal length of the lens system L1. A detector and high NA lens areplaced at the pupil plane. The pupil plane may be re-imaged withauxiliary optics since the pupil plane of a high NA lens is usuallylocated inside the lens.

The pupil plane of the reflector light is imaged on the CCD detector 32with an integration time of, for example, 40 milliseconds per frame. Inthis way, a two-dimensional angular scatter spectrum of the substratetarget 6 is imaged on the detector 32. The detector 32 may be, forexample, an array of CCD detectors or CMOS detectors. The processing ofthe spectrum gives a symmetrical detection configuration and so sensorscan be made rotationally symmetrical. This allows the use of a compactsubstrate table because a target on the substrate 6 can be measured atany rotational orientation relative to the sensor. All the targets onthe substrate 6 can be measured by a combination of a translation and arotation of the substrate 6.

A set of interference filters 30 may be available to select a wavelengthof interest in the range of, say, 405-790 nm or even lower, such as200-300 nm. The interference filter may be tunable rather than includinga set of different filters. A grating could be used instead of one ormore interference filters.

The substrate 6 (or even the reflective surface 34) may be a grating.The grating may be printed such that after development, a series of barsare formed of solid resist lines. The bars may alternatively be etchedinto the substrate. This pattern is sensitive to comatic aberrations ina lithographic projection apparatus, particularly the projection systemPL, and illumination symmetry and the presence of such aberrations willmanifest themselves in a variation in the printed grating. Accordingly,the scatterometry data of the printed gratings is used to reconstructthe gratings. One or more parameters of the grating, such as line widthsand shapes, may be input to the reconstruction process from knowledge ofthe printing step and/or other scatterometry processes.

The scatterometer may be used to detect the spectrum and create asymmetrical pupil plane image from which the discontinuities can bemeasured and one or more grating properties therefore calculated.

The scatterometer may be adapted to measure the overlay of twomisaligned periodic structures by measuring asymmetry in the reflectedspectrum, the asymmetry being related to the extent of the overlay. Thescatterometer may be adapted to measure the overlay of two misalignedgratings or periodic structures by measuring asymmetry in the reflectedspectrum and/or the detection configuration, the asymmetry being relatedto the extent of the overlay. Due to the symmetrical detectionconfiguration, any asymmetry is clearly distinguishable. This provides astraightforward way to measure misalignment in the gratings.

One type of substrate pattern used is shown in FIG. 4. A referencegrating 14 has a measurement grating 12 printed on top of it (or on topof a dielectric layer 16 which is made on top of the grating 14). Theamount by which the measurement grating 12 is offset with respect to thereference grating 14 is known as the overlay 22, as indicated in FIG. 4.

Note that the radiation source 2 may illuminate the object symmetricallywith respect to the surface normal and the scatterometry detectormeasures scatter radiation from several angles, although a source 2which illuminates the object from an oblique angle is also possible.

Overlay metrology is based on the measurement of an asymmetry in theangular scatter spectrum. Symmetric structures yield symmetric angularspectra and an asymmetry in the target shows up as an asymmetry in theangular scatter spectrum. This property is the basis of overlaymetrology using angle-resolved scatterometry.

Two overlapping but misaligned gratings (measurement grating 12 andreference grating 14) made of bars (or line elements) 18 with a width 20(see FIG. 4) form one composite asymmetric target. The resultingasymmetry in the angular scatter spectrum is detected with theangle-resolved scatterometer 4 shown in FIG. 3 and used to derive theoverlay 22.

In known production methods for devices using a lithographic apparatus,the targets for various measurements, especially the overlay measurementgratings 12 as described above, are positioned on different positions inthe scribe lane spaces 15 of a substrate 6, i.e. between the parts ofthe substrate 6 wherein the devices are formed by various processes.Each target 12 for a specific measurement is located in another positionthan the target used in an earlier measurement, e.g. in a cascade formas shown in FIG. 5 a with positions A-F. This requires a lot of realestate in the scribe lane 15, as for producing a device, as many asfifteen or even twenty layers need to be processed, and consequently,fifteen or even twenty positions A-F are needed.

According to an embodiment of the present invention, only a limitednumber of positions A-C of targets is necessary, as shown schematicallyin FIG. 5 b. This is made possible by obscuring earlier measurementtargets using a grid 17 of conducting material, having grid openingssmaller than the measurement radiation wavelength. The term wavelengthas used in this description refers to the effective wavelength in themedium where the grid 17 is located, e.g. in a water layer as explainedabove referring to immersion lithography, which may be different from afree space wavelength. An embodiment is shown schematically in FIG. 6,and includes a grid 17 of lines of conducting material, wherein thedistance d between the lines is smaller than the measurement radiationwavelength λ. The distance d between the lines is e.g. in the order ofmagnitude of 500 nm, using lines (or wires) with a width of e.g. 100-200nm.

In this manner, a kind of Faraday shield is formed, which obscuresearlier measurement targets for the measurement radiation wavelength λ,thus allowing re-use of the specific location for later measurements. Inone embodiment, the conducting material is a metal, which would allowall processes using a metal deposition or the like to form a grid on themeasurement location, e.g. backend processes in which vias are producedon the substrate 6, metal conductors, or bonding pads, or in processeswherein metallic gates are produced. The present invention is alsoapplicable for processes in which doped semiconductor material layersare formed, as these also allow to produce the conducting grid 17according to the present invention.

The grid 17 may also have another appearance, e.g. a rectangular fieldcovering the earlier measurement target, provided with circular openingswith a diameter smaller than the measurement radiation wavelength λ.

In an embodiment of the present invention, only three positions areneeded for measurement targets. This is clarified with reference to thesectional view of a part of a substrate 6 as shown in FIG. 7. In a firstlayer 11 a, a reference grating 14 a is made on a first position A usingknown processes, and after finishing this first layer 11 a, ameasurement grating 12 a can be printed on top of the reference grating14 a and measurements executed for a second layer 11 b (e.g. overlaymeasurements). After finishing measurements in the second layer 11 b,this second layer 11 b may be processed, wherein a reference grating 14b for measurements associated with a third layer 11 c is produced on asecond position B in the scribe lane space. Again, a measurement grating12 b is printed on top of the reference grating 14 b, and measurementsare carried out. Next, the third layer 11 c is processed, by forming anext reference grating 14 c on third position C, but also, a grid 17 ais formed on position A, thus shielding the underlying measurementgrating 12 a and reference grating 14 a. Measurement grating 12 c may beprinted on top of reference grating 14 c, and measurements may beexecuted associated with a fourth layer 11 d.

Now however, as a result of the grid 17 a in the third layer 11 c, afurther reference grating 14 d may be formed in the fourth layer 11 d onposition A. Also, a grid 17 b is formed on second position B, in orderto obscure the underlying measurement grating 12 b and reference grating14 b. This may be repeated for each next layer, and only three positionsA-C are necessary for the measurement targets 12, 14.

As mentioned above, the various embodiments may be used in associationwith overlay measurement targets, which each require a reference grating14 in a substrate layer and a measurement grating 12 printed on top ofthe reference grating 14. The various embodiments may also be used inassociation with other types of measurements, which may even use othertypes of measurement targets, such as critical dimension (CD)measurements or alignment measurements. For example, in the case ofalignment measurements, alignment marks are being used in a singlelayer. These alignment marks may be obscured using a grid 17 accordingto the present invention in a layer above the (undeveloped) alignmentmark.

The grid 17 according to any one embodiment described above is appliedin the scribe lane space 15 of the substrate 6. In a finished substrate6 or wafer, and even in the edge area of finished dies, this grid 17 isstill present and visible. Thus the use of the present method is alsovisible in a device manufactured according to embodiments of the presentinvention.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. It should be appreciated that, in the context of suchalternative applications, any use of the terms “wafer” or “die” hereinmay be considered as synonymous with the more general terms “substrate”or “target portion”, respectively. The substrate referred to herein maybe processed, before or after exposure, in for example a track (a toolthat typically applies a layer of resist to a substrate and develops theexposed resist), a metrology tool and/or an inspection tool. Whereapplicable, the disclosure herein may be applied to such and othersubstrate processing tools. Further, the substrate may be processed morethan once, for example in order to create a multi-layer IC, so that theterm substrate used herein may also refer to a substrate that alreadycontains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus arranged to transfer a pattern from apatterning device onto a substrate, wherein the lithographic apparatusis configured to: provide a measurement target on the substrate toenable a substrate measurement for a specific process using awavelength; and dispose a grid of conducting material over themeasurement target, wherein the grid has grid openings which are smallerthan the wavelength.
 2. The lithographic apparatus of claim 1, whereinthe conducting material is a metal.
 3. The lithographic apparatus ofclaim 1, wherein the conducting material is a doped semiconductormaterial.
 4. The lithographic apparatus of claim 1, wherein the grid ofconducting material is disposed over the measurement target during afurther processing of the substrate.
 5. The lithographic apparatus ofclaim 1, wherein the substrate measurement comprises an overlaymeasurement, critical dimension measurement, or alignment measurement.6. A device manufacturing method comprising transferring a pattern froma patterning device onto a substrate, the method comprising: providing ameasurement target on the substrate to enable execution of a substratemeasurement using radiation of a wavelength; and disposing a grid ofconducting material over the measurement target, wherein the grid hasgrid openings which are smaller than the wavelength.
 7. The devicemanufacturing method according to claim 6, wherein the conductingmaterial is a metal.
 8. The device manufacturing method according toclaim 6, wherein the conducting material is a doped semiconductormaterial.
 9. The device manufacturing method according to claim 6,wherein the disposing is executed during a further processing of thesubstrate.
 10. The device manufacturing method according to claim 6,wherein the substrate measurement comprises an overlay measurement,critical dimension measurement, or alignment measurement.
 11. A devicemanufactured according to a method, the method comprising: providing ameasurement target on the substrate to enable execution of a substratemeasurement using radiation of a wavelength; and disposing a grid ofconducting material over the measurement target, wherein the grid hasgrid openings which are smaller than the wavelength.